Notorious bad boy Charlie Sheen has made headlines over the years for his off-screen antics, most recently for his belligerent tantrum at New York's Plaza Hotel. On Friday, CBS Chief Nina Tassler spoke publicly about the Two and a Half Men star: "I have a high level of concern. How could we not?" Referring to Sheen’s hit show, she added, "You can't look at it simplistically. Charlie is a professional. He comes to work. He does his job very well." Sheen's reps have yet to comment on Tassler's announcement. CBS and Warner Bros. quietly expressed concern about Sheen and the series earlier this week, and a story was leaked that they allegedly considered canceling the sitcom to give Sheen the opportunity to seek help.